Public cellular mobile radio networks such as GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telecommunication System) networks have limited communication resources due to the principle involved. In general, these networks are designed in such a manner that the average volume of communication can be granted without restriction. Due to special situations, however, it may occur that a volume of communication requests of above-average level produces a regional or even global capacity utilization of these mobile radio networks. This is the case, for example, with major events or sports events such as world championships or Olympiads or also in catastrophe situations, for example triggered by natural catastrophes. In such situations, the network capacities can be overloaded. The mobile radio networks are therefore set up in such a manner that further call requests are declined when resources are almost or completely used up.
However, it is helpful and in some cases also required, especially in the said situations, that certain mobile radio subscribers such as rescue forces, police, fire departments but also serving members of the mobile radio undertaking operating the mobile radio network obtain secure network access even in the case of networks utilized to capacity. In this context, it must be differentiated that these selected mobile radio subscribers, on the one hand, can convey their access request to the mobile radio network and are not already blocked for an access by the network or rejected and, on the other hand, are assigned the resources necessary for setting up a telecommunication link, for example a free channel.
In GSM and UMTS networks, there is the possibility of prioritizing selected mobile radio terminals, that is to say certain subscribers, compared with other ones. In overload situations in a mobile radio network, prioritized mobile radio terminals or subscribers are treated preferentially compared with non-prioritized mobile radio terminals or subscribers. This enables these subscribers to set up calls even in overload situations. Various methods and standards which have been developed by the 3GPP (Third Generation Partnership Project) are known for technically implementing such prioritizations.
To ward off overload situations in a mobile radio network, a so-called “Access Class Barring” function is used in GSM and UMTS mobile radio networks. It regulates that certain mobile radio terminals are allowed or prohibited from accessing the mobile radio network. In this case, access classes are defined and allocated to the terminals. According to the 3GPP TS 22.011 standard, 16 such access classes are provided. The access class of a subscriber is stored on the SIM (Subscriber Identity Module) or USIM (Universal Subscriber Identity Module) card of the terminal. Classes 0 to 9 are provided for the normal subscribers, classes 11 to 15 are reserved for special subscribers. Thus, for example, class 12 is reserved for security services, class 13 for public supply facilities such as water, power or gas suppliers, class 14 for emergency rescue services such as police and fire departments and classes 11 and 15 for serving members of the mobile radio network operator. The possibility exists that a mobile radio terminal or subscriber has an allocation both to one of classes 0 to 9 and to one of the special classes 11 to 15. Class 10 allows emergency calls and is allocated to each SIM/USIM card. A mobile radio operator is obliged to pay attention when issuing the SIM/USIM cards that the individual access classes 0 to 9 are distributed more or less evenly.
Overload situations are now combated by blocking access classes 0 to 9 on a random basis so that all regular mobile radio subscribers are “disadvantaged” to the same extent when the capacity of the network is overloaded. This means that subscribers with a terminal in which the SIM/USIM card only has allocation to one of classes 0 to 9 are blocked at least temporarily, if necessary, and cannot access the mobile radio network. These terminals cannot therefore set up incoming or outgoing calls.
One possibility for implementing subscriber prioritization is known by the network function “enhanced multi-level precedence and preemption” (eMLPP) and described in specification 3GPP TS 22.067. It guarantees network access even in the case of a blockage, for example due to occupancy of all channels, implements a so-called queue management in which network resources are provided in dependence on priority and regulates the priority of new calls, for example of an emergency call, compared with current calls of lower priority which are displaced by calls of higher priority. In the case of eMLPP, up to seven different priority stages are possible which are defined by eMLPP parameters by means of which a simple allocation of a certain priority stage to the subscribers is possible. The parameters are stored in the home location register (HLR), on the SIM/USIM card of the terminal and/or the mobile switching center (MSC).
However, the eMLPP method does not provide for calls to subscribers which are not allowed to access the network due to the “Access Class Barring”. It can only be applied, therefore, if the called subscriber is allowed to communicate with the network. In other words, a subscriber whose terminal is blocked by the “Access Class Barring” cannot communicate with the network even by prioritization of the call by means of the eMLPP functionality.